The invention relates to a process for the production of slag sand (granules) from blast-furnace slag by granulation of the slag by means of jetting water in a spray head into the slage jet, the resulting granules/water mixture being dewatered in a downstream dewatering unit, the granules being fed to a distribution unit and the process water, after making up the losses caused by vaporization and the residual moisture remaining in the granules, being recycled to the spray head and the vapours and gases formed on granulation being collected in a space above a granules/water mixture receiver, and to advantageous equipment for carrying out the process.
It is known that, in the conversion of iron ore to crude iron in a blast-furnace, blast-furnace slag is formed to a considerable extent in addition to the molten crude iron. On each tapping, a quantity of slag is formed, the weight of which corresponds to approximately one third of the weight of the crude iron, whereas the volume fraction of the slag, because of the lower density of the slag, is greater than the volume fraction of crude iron.
Various processes are known for producing high-grade granules with a high percentage of glassy constituents, uniform grain structure and good grindability from blast-furnace slag by granulation of the molten slag directly at the blast-furnace. The granules formed can then be put into intermediate storage for further processing into building materials and transported away.
An important step in the processing of the granules is dewatering. For this purpose, various processes and types of equipment are known (German Patent Specification No. 1,583,949, German Patent Specification No. 2,260,924) as well as modern dewatering machines with bucket wheels, wherein the slag sand/water mixture is dewatered to a low residual moisture content and the process water is recycled for reuse (German Offenlegungsschrift No. 2,749,143, German Offenlegungsschrift No. 2,807,441 and German Offenlegungsschrift No. 2,911,903). In these known processes, the slag granulation was effected by spraying the molten slag at about 1500.degree. C. by means of a propulsion jet, consisting of many individual jets, from a spray head at a temperature of 35.degree.-40.degree. C. and thus processing it to give fine granules. The water vapour arising in this process contains large quantities of H.sub.2 S and H.sub.2 O, in particular when sulphur-containing ores are used. The fractions of the pollutants H.sub.2 S and SO.sub.2 contained in the water vapour formed on quenching of the slag have hitherto been discharged in the vapour via a stack.